3.3 Value of Digestive Activities as Biomarkers in Two
Aquatic Invertebrates: Application to the Seine River
Basin
3.3.1 Introduction
All of the biochemical and physiological processes involved in the life cycle of
organisms are closely related to energy metabolism. The energy contributions of
individuals are determined, among other processes, by their ability to transform raw
energy ingested in the form of food into assimilable energy in the form of nutrients.
This ability depends in particular on digestive enzyme activities, notoriously sensitive to various chemical stressors [51]. Disruption of digestive processes may affect
individual energy balance and result in energy allocation disturbances with possible
consequences on individual fitness. Moreover, as part of an environmental quality
assessment, variations in enzymatic activities are often one of the first responses to
stress; they therefore represent useful points to confirm the occurrence of toxic
effects before they are perceptible at higher levels of biological organisation. The
PIREN-Seine programme provided the opportunity to study the activity of digestive
enzymes in two aquatic organisms largely used in ecotoxicology, the zebra mussel
(D. polymorpha) and the gammarid (G. fossarum). This work involved both the
characterisation of the studied response variability with respect to biotic and abiotic
factors and the application of these tools in the Seine River watershed.
3.3.2 Characterisation of Digestive Enzyme Activities
The response of biomarkers might be influenced by environmental factors (both
biotic and abiotic), potentially confounding factors that may complicate interpretation of the results. It thus appears necessary to determine the sources of variations,
the amplitude of the response modulations related to these confounding factors with
respect to the contamination factors, and to specify the measurement conditions of
these biomarkers.
In the gammarid, previous experiments conducted under controlled conditions
made it possible to study the effects of (1) temperature and conductivity; (2) breeding
and moulting cycles in the female; and (3) the quantity of available food [52]. The
results indicate that conductivity is not a key parameter influencing the digestive
enzyme activities during short-term bioassays. Conversely, temperature must be
taken into account for reliable data interpretation, especially in environments with
temperatures below 12
C [52]. In addition, amylase, cellulase and trypsin activities
in females decreased significantly during the reproductive cycle, particularly during
the amplexus. In contrast, gammarid males retain higher levels of digestive activity
during this breeding season and therefore appear to be unaffected by the development cycle. Finally, the application of trophic stress decreases the activity of
amylase, which is observed in both females and males [53].
Experience Gained from Ecotoxicological Studies in the Seine River and. . .
253
Aquatic Invertebrates: Application to the Seine River
Basin
3.3.1 Introduction
All of the biochemical and physiological processes involved in the life cycle of
organisms are closely related to energy metabolism. The energy contributions of
individuals are determined, among other processes, by their ability to transform raw
energy ingested in the form of food into assimilable energy in the form of nutrients.
This ability depends in particular on digestive enzyme activities, notoriously sensitive to various chemical stressors [51]. Disruption of digestive processes may affect
individual energy balance and result in energy allocation disturbances with possible
consequences on individual fitness. Moreover, as part of an environmental quality
assessment, variations in enzymatic activities are often one of the first responses to
stress; they therefore represent useful points to confirm the occurrence of toxic
effects before they are perceptible at higher levels of biological organisation. The
PIREN-Seine programme provided the opportunity to study the activity of digestive
enzymes in two aquatic organisms largely used in ecotoxicology, the zebra mussel
(D. polymorpha) and the gammarid (G. fossarum). This work involved both the
characterisation of the studied response variability with respect to biotic and abiotic
factors and the application of these tools in the Seine River watershed.
3.3.2 Characterisation of Digestive Enzyme Activities
The response of biomarkers might be influenced by environmental factors (both
biotic and abiotic), potentially confounding factors that may complicate interpretation of the results. It thus appears necessary to determine the sources of variations,
the amplitude of the response modulations related to these confounding factors with
respect to the contamination factors, and to specify the measurement conditions of
these biomarkers.
In the gammarid, previous experiments conducted under controlled conditions
made it possible to study the effects of (1) temperature and conductivity; (2) breeding
and moulting cycles in the female; and (3) the quantity of available food [52]. The
results indicate that conductivity is not a key parameter influencing the digestive
enzyme activities during short-term bioassays. Conversely, temperature must be
taken into account for reliable data interpretation, especially in environments with
temperatures below 12
C [52]. In addition, amylase, cellulase and trypsin activities
in females decreased significantly during the reproductive cycle, particularly during
the amplexus. In contrast, gammarid males retain higher levels of digestive activity
during this breeding season and therefore appear to be unaffected by the development cycle. Finally, the application of trophic stress decreases the activity of
amylase, which is observed in both females and males [53].
Experience Gained from Ecotoxicological Studies in the Seine River and. . .
253